1. Field of the Invention
This invention relates to a filter for the continuous industrial-scale filtration of gases laden with solid particles.
2. Description of the Related Art
Existing industrial filters which are intended for the filtration of gases laden with solid particles with sufficient gas flow rate and sufficiently good retention efficiency are limited as regards the maximum service temperature. The maximum service temperature is approximately 330.degree. C. for an electrostatic filter and approximately 180.degree. C. for a cloth filter.
Existing industrial dust filters do not allow filtration at very high temperatures of gases which contain chemically aggressive substances such as the oxides of sulphur, chlorine and other constituents.
Moreover, tubular porous filtering elements which may, especially, serve to remove dust from hot gases are known. Such "multiple tube filters" as described, for example, in the document EP-A-0,317,190 per se withstand high temperatures (even up to 1600.degree. C. or more).
Hitherto, the use of these multiple tube filters was limited, on the one hand, to relatively small filters which are intended for laboratory filtration and incorporate only a limited number of multiple tube filters (and which are therefore suitable only for quite low gas flow rates) and, on the other hand, to larger filters for the industrial-scale filtration of gases (with higher gas flow rates), but these larger filters only withstand temperatures which do not exceed 450.degree. C.
To date, there is no device in existence which is sufficiently thermally stable and allows the industrial-scale filtration of gases at high temperatures, for example from 500.degree. to 900.degree. C.
The production of an industrial gas filter for high gas flow rates which can withstand such high temperatures creates serious problems originating, especially, in the expansion tensions which it is difficult to avoid in the presence of significant variations in temperature.
These problems are further complicated if the filter is to be used for the high-temperature filtration of gases containing chemically aggressive substances (such as hot flue gases which contain chlorine, sulphur and fluorine).
Hitherto, no satisfactory solution to these problems has been provided.
In various industrial processes, the filtration of gases laden with solid particles at high temperature could, however, be very useful and beneficial.
This is especially the case for eliminating from hot flue gases the substances which could damage the environment by polluting the atmosphere. The filtration of hot gases may also make it possible to recover precious substances, such as precious metals, in processes which are carried out at high temperature.
It should be pointed out that the cooling of hot gases laden with particles, before filtration thereof, does not always constitute a satisfactory or beneficial solution.
One of the reasons for this is that condensation products and even new products which are undesirable may form in some cases upon the cooling of hot gases laden with particles.
Unacceptable amounts of energy may also be lost during cooling processes.